Improve the hashability of exceptions when they contain hashable data.

Refs: python-jsonschema/jsonschema#1126

docs/changes.rst

@@ -2,6 +2,12 @@
 Changelog
 =========
 
+v0.29.2
+-------
+
+* Improve the hashability of exceptions when they contain hashable data.
+
+
 v0.29.1
 -------
 

referencing/exceptions.py

@@ -30,6 +30,9 @@ def __eq__(self, other: Any) -> bool:
             return NotImplemented
         return attrs.astuple(self) == attrs.astuple(other)
 
+    def __hash__(self) -> int:
+        return hash(attrs.astuple(self))
+
 
 @frozen
 class NoInternalID(Exception):
@@ -49,6 +52,9 @@ def __eq__(self, other: Any) -> bool:
             return NotImplemented
         return attrs.astuple(self) == attrs.astuple(other)
 
+    def __hash__(self) -> int:
+        return hash(attrs.astuple(self))
+
 
 @frozen
 class Unretrievable(KeyError):
@@ -58,6 +64,14 @@ class Unretrievable(KeyError):
 
     ref: URI
 
+    def __eq__(self, other: Any) -> bool:
+        if self.__class__ is not other.__class__:
+            return NotImplemented
+        return attrs.astuple(self) == attrs.astuple(other)
+
+    def __hash__(self) -> int:
+        return hash(attrs.astuple(self))
+
 
 @frozen
 class CannotDetermineSpecification(Exception):
@@ -70,8 +84,16 @@ class CannotDetermineSpecification(Exception):
 
     contents: Any
 
+    def __eq__(self, other: Any) -> bool:
+        if self.__class__ is not other.__class__:
+            return NotImplemented
+        return attrs.astuple(self) == attrs.astuple(other)
 
-@attrs.frozen
+    def __hash__(self) -> int:
+        return hash(attrs.astuple(self))
+
+
+@attrs.frozen  # Because here we allow subclassing below.
 class Unresolvable(Exception):
     """
     A reference was unresolvable.
@@ -84,6 +106,9 @@ def __eq__(self, other: Any) -> bool:
             return NotImplemented
         return attrs.astuple(self) == attrs.astuple(other)
 
+    def __hash__(self) -> int:
+        return hash(attrs.astuple(self))
+
 
 @frozen
 class PointerToNowhere(Unresolvable):

referencing/tests/test_exceptions.py

@@ -5,17 +5,30 @@
 from referencing import Resource, exceptions
 
 
-def pairs(*choices):
+def pairs(choices):
     return itertools.combinations(choices, 2)
 
 
-@pytest.mark.parametrize(
-    "one, two",
-    pairs(
-        exceptions.NoSuchResource("urn:example:foo"),
-        exceptions.NoInternalID(Resource.opaque({})),
-        exceptions.Unresolvable("urn:example:foo"),
-    ),
+TRUE = Resource.opaque(True)
+
+
+thunks = (
+    lambda: exceptions.CannotDetermineSpecification(TRUE),
+    lambda: exceptions.NoSuchResource("urn:example:foo"),
+    lambda: exceptions.NoInternalID(TRUE),
+    lambda: exceptions.InvalidAnchor(resource=TRUE, anchor="foo", ref="a#b"),
+    lambda: exceptions.NoSuchAnchor(resource=TRUE, anchor="foo", ref="a#b"),
+    lambda: exceptions.PointerToNowhere(resource=TRUE, ref="urn:example:foo"),
+    lambda: exceptions.Unresolvable("urn:example:foo"),
+    lambda: exceptions.Unretrievable("urn:example:foo"),
 )
+
+
+@pytest.mark.parametrize("one, two", pairs(each() for each in thunks))
 def test_eq_incompatible_types(one, two):
     assert one != two
+
+
+@pytest.mark.parametrize("thunk", thunks)
+def test_hash(thunk):
+    assert thunk() in {thunk()}